a) Field of the Invention
The invention relates to an adjustable steering column for a motor vehicle, with a setting unit displaceable into at least one displacement direction for setting the position of the steering column, a holding unit nondisplaceable into this displacement direction, a securement device, in the opened state of which the setting unit is displaceable with respect to the holding unit for setting the position of the steering column and in the closed state of which the setting unit is secured in position by the securement device, and a crash blocking device, which is displaceable between a passive state, in which the setting unit is displaceable with respect to the holding unit in the opened state of the securement device for setting the position of the steering column, and an active state, in which the crash blocking device raises an additional holding force against a displacement of the setting unit with respect to the holding unit into at least one displacement direction.
b) Description of Related Prior Art
Adjustable steering columns serve to increase the convenience and comfort of the driver and can be changed with respect to length, height, and/or angular position in order to be able to adapt in this way the position of the steering wheel to the seating position of the driver. To do this, these steering columns include a setting part whose position with respect to a holding part can be changed and be secured in position with a securement device or a clamping system. The case in which the setting part is secured in position with respect to the holding part can be considered to be the normal operating state since the motor vehicle is only intended to be driven in this state.
In adjustable steering columns the problem is encountered that in the event of a crash the uncontrolled dislocation of the steering column must be prevented so that, for example, sufficient retaining force for opening the airbag is available and/or the energy upon the impact of the driver onto the steering wheel can be dissipated under control. The securement device simultaneously is to be smooth in operation and capable of being opened and closed with short strokes of the actuation members and is to assume only a small installation space.
For securing the set position, EP 0 802 104 B1 for example proposes intersecting lamella disk packs, wherein the first one is connected on the setting part, here a jacket unit, supporting the steering spindle, and the second one on the holding part connected to the vehicle chassis. The two intersecting lamella packs are penetrated by a clamp bolt and tightened against one another by the actuation of a clamping lever. In order for the steering column to be adjusted, the lamellae have elongated holes oriented in the adjustment direction of the steering column, the elongated holes being oriented identically in all lamellae of a lamella pack.
These systems already permit securement in position of the steering column with few lamellae and a short actuation stroke and a relatively low clamping force. However, in order to be able to absorb the high holding forces such as are required in the event of a crash, the number of lamellae and/or the clamping force must be increased. The securement device becomes thereby more complicated, more expensive and requires more installation space. Furthermore, the strokes and forces for the actuation of the clamping lever become greater. The energy dissipation, moreover, can only be set imprecisely during the slipping-through of the securement device.
EP 0 836 981 proposes, for example, to secure the set position to bring a toothed rack, fastened on a carrying unit connected with the vehicle chassis, into engagement with a second toothed rack fastened on the jacket unit accepting the steering spindle. To adjust the steering column, these toothed racks are brought out of engagement so that adjusting the steering column becomes possible.
In order for such systems not to slip through in the event of a crash, the toothings must be laid out appropriately sturdily and sufficient clamping force must be provided such that the toothings do not come out of engagement. Therewith the strokes and forces for actuating the clamping lever become greater. Moreover, a sturdy layout of the toothing demands that the tooth intervals become greater, wherein the step width, in which the steering column can be adjusted, increases. However, for convenience and comfort it is desirable to make possible an adjustment which is as continuous as possible or is at least closely stepped.
Both of the described principles, moreover, require a very high rigidity of the vehicle body-side carrying unit.
DE 196 17 561 C1 therefore proposes, in addition to the securement device, a crash blocking device with an additional arrest part, which acts independently of the securement device and, in the event of a crash, raises an additional holding force.
However, the disadvantage of this solution is that such additional arrest part must be provided which demands additional installation space and expenditures. It must further be ensured that such an additional arrest part in the event of a crash, but only in this event, comes reliably into engagement and, for the case that the steering column is to be adjusted, is reliably brought out of engagement.
EP 1 433 687 A2 discloses providing a canted part acting upon a deformation of the steering column in the event of a crash, which part after it has been canted applies an additional holding force against a displacement of the set position of the steering column. For this canted part to become effective, however, depends on the deformation of the steering column in the event of a crash.
The adjustable steering column disclosed in DE 195 06 210 C1 comprises a blocking member with a blade edge which can be pressed against a clamping flange when closing the securement device. In the event of a crash the blade edge of this blocking member digs into the material of the clamping flange in order to bring about as form-fittingly a locking as possible of the jacket unit of the steering column with the holding unit stationary on the vehicle body.
DE 41 33 960 C2 describes a safety arrangement for motor vehicle steering columns, wherein the end of the steering column facing the driver is shifted forwardly in the event of a crash. For this purpose a swivellable (cutting) edge holder is provided on which pressure or tension means, for example pyrotechnical arrangements, attack. In the event of a crash, the cutting edge of the edge holder penetrates into a jacket tube of the steering spindle or into the steering spindle.